Determination of moisture in gases



April 22, 1952 c. a. HAYwoRTH DETERMINATION OF' MOISTURE IN GASES 2 SHEETS- SHEET l Filed Jan. 22, 1949 @N AI HIM um April 22, 1952 c. B. HAYwoRTH 2,594,163

DETERMINATION OF MOISTURE IN GASES Filed Jan. 22, 1949 2 SI-IEETS-SI-IEET 2 INVENTOR. CURTIS B. HAYWORTH Bym:

ATTORNEY.

Patented Apr. 22, 1952 UNITED STATES PATENT OFFICE",

DETERMINATION F MOISTURE IN GASES Curtis B. Hayworth, New York, N. Y., assignor to Allied Chemical & Dye Corporation, New York, N. Y., a corporation of New York Application January 22, 1949, Serial No. 72,130

(Cl. 'I3-29) 4 Claims.

This invention relates to amethod and ap- I was withdrawn, i. e. spot information concerning theV actual moisture conditions, but failed to tell how the process was functioning between graviinetric tests.

A primary object of the present invention is to provide an improved method and apparatus for obtaining accurate measurements of the moisturecontent oi gases'in a more rapid and eillcient mannerthan has hitherto been attained.

Another object of the invention is to provide a method and means of determining electrical conductivity of a hygroscopic material in contact with gases containing moisture as an index of the moisture content in the gases.

' A further object of the invention is to provide a continuous method of measuring changes in moisture content in gases of varying composition. Y

Another object of the invention is to. provide a method and means for determining moisture .content of gases containing corrosive substances such as sulfur dioxide. Y

A further object of the invention is to provide a method and apparatus for measuring moisture in gases having a low concentration of water.

Another object of the invention is to provide a device for continuously measuring moisture in gases which is simple and economical in construction and which will operate for long periods of time without undue attention.4 l

Other objects and advantages of the invention will be apparent from the following description and accompanying drawings.

A preferred method of practicing the process in `accordance with the present invention comprises passing a gas containing moisture in contact with a film of hygroscopic material suspended between two electrodes, maintaining the lgas during its contact with the lm of hygro- 2 scopic material at a constant temperature vand electrically determining the conductivity ofthe iilm of hygroscopic material.

A preferred form of apparatus for carrying out the present invention comprises a housing hav.- ing a gas inlet and gas outlet, a heating jacket surrounding the housing for. thermostatically maintaining a constant temperature therein, a conductivity cell contained in the housing supporting two narrowly spaced electrodes, a iilm of hygroscopic material suspended between the electrodes which lm is exposedl to the moisture containing gases passing through the housing thereby varying the moisture content of the hygroscopic material with changes in moisture content of the gases passing therethrough,and electrical measuring means for determining the con- 4ductivity of the iilm of hygroscopic material.

' Referring to the drawings, Figure 1 diagrammatically represents the complete unit assembly of the moisture recording apparatus. Figure 2 1s an isometric view of the conductivity cell in Vpartial section.

The various parts making up the assembly of the recording apparatus of Figure 1 are gas inlet passage of liquid into vthe recording apparatus, l

-inlet 4 which conducts the gas to housing 5,. conductivity cell 6 having mounted thereon electrodes l, leads 8 connected to recorder 9 which in turn through leads II are connected to 110 volts cycle alternating current, thermostat `well `I2 into which is inserted thermostat I3 extendingwinto housing 5,`l mercury I4 filling the bottom portion of thermostat well I2, temperature control jackets I5 and I6 surrounding housing 5, leads Il leading from thermostat I3 to relay I8 which connects to temperature control `jackets I5 and I6 by means of leads I9, 2|, 22, 23 and resistance elements 24 and 25, leads 2B connected to volts 60 cycle alternating current for supplying heatto temperature control `jackets I5 and I6 and for activating relay I8.

gas exhaust conduit 21, moisture trap 28 and gas outlet 29. l

The conductivity cell 6 (Figure 2) consists oi Pyrex glass tubing open at one endl about 12 mm. in diameter and about 200 mm. long. Two platinum wires 3| about 24 gauge thicknesslcovered by glass shields 32 extend inside tulbe 6 along its length passing through the glass wall of tube E at points 33 and 34 with the terminal points sealed to the top of the glass surface at points 35 and 36 in such manner to form a pair ofV parallel rectangular planes extending about mm. in height above the surface of tube (i.v Electrodes 'I between which a drop of hygroscopic material is suspended are approximately mm. long and spaced by a distance of 0.5 to 1 mm. Passages 33 and 34 through which platinum wires 3| pass through 'the wall of tube 5 are sealed'to prevent the leakage of any gas or moisture'into tube 6. Likewise near the open end of tube 6 a glass plate 31 is welded to shields 32 and the inner wall of tube 6to seal that end of the tube from the atmosphere. Also the ends of shields32 extending beyond plate 31 are sealed to platinum wires 3I to prevent any leakage 'through'openings ing 5 (Figure 1) surrounds tube 6 and is welded thereto. v Y

Installation of conductivitycell `and housing 5 is as follows: The position `of platinum wire electrodes Tis adjusted so that they are straight, Parallel `Yandabout10.5 to 1.0 mm. apart. This can'best'be done by inserting a razor blade between them pressing the wires against it with a pair of ivory tipped forceps and then cautiously removing the blade. Care must be exercised to 'avoid'chipping glass Vfrom seals 33 and 34 which might "result in cutting or kweakening lof the platinum "wire, Clean the Velectrodes in warm chromic acid, rinse with distilled water and dry witha'cetone. insert the conductivitycell into housing 5 .temporarily for protection. Fasten heating jacket I5 and I6, the latter provided with an opening through which Vwell I2 extends. armlndhousillg 5 in such'mannerthat gas enteringinlet 4 is preheated tothe desired temperature by jacket I5 `and'maintained at that temperature vduring itsI contactwith the rhygroscopic material'by jacket I6.

The assembly is now ready for 'installation in the Splant ywhere it is required 'for testing Vthe moisturecontent of gases. The assembly must be Amounted rigidly `so vthat vit cannot vbe moved or rotated,`either of which might break 'the'hyvgroscopic f'film, and should be'protected'by housing 'in'f'a cabinet with provision for removing the conductivity cell 6 for inspection or reloading withoutdisturbing the rest of Vthe apparatus. The thermostatfwell I2 should be in van upright posi- 'tion as shown in :Figure 1. Y The electrolyte may be prepared,'fo'r example,

by 'spreading about 0.2 gram of phosphorus pentoxide ona watch glass and allowing it to absorb `just'enough vmoisture to liquey. If it is vpermitted is transferred to 'electrodes 1 so that a fili-nis u formed inlthe space'betweenthem.V Thereafter immediately reinsert cell 6 in housing 5 with electrodes 'I facing upwards towards thermostat well I 2 asshown in Figure `1.

About Z'cc. of'rnercury are poured into thermostat well 'I2and then thermostat I3 inserted into the well. Thermostat leads I1 are'connectedto conventional relay I8 which in turn are connected vin'circuit'with heating jackets I5 and lfthrough leads I9, 2|, 22 and 23 and resistance elements 24 and 25, 100 Vand`200 watt lamps, respectively,

having the usual pairs of resistance arms, onel arm consisting of the electrolyte suspended between electrodes 1, and a galvanometer for measuring the degree of unbalance in the bridge circuit and thereby changes in resistance of the iilm'of electrolyte. The Wheatstone bridge and its operation in connection with measuring changes in resistance are well known to those skilled in the art. Various refinements have been added to the Wheatstone bridge making possible instantaneous recordings of changes in the resistance of a variable resistance element. Such instruments aref commonly designated in industry as Micromax recorders. Any ksuitable 'means for recording the resistance Lof the hygroscopic material between electrodes 'I may be employed in the practiceof my invention. e

A'sample line may be connected from a plant containing gas whose `moisture content `isto be determined to gasvinlet I at Va point in the plant vwhere there is F positive pressure; thereby slow leaks in the system become relatively Yunimpc'n'tant and -no pumping equipment `is necessary. VFlow meter2 maybe of the -usual -Ushaped 'tube containing aliquid and should be calibrated by means cfa wet te'st meter. 1n the'pa'rticular apparatus being described with glass cell housing 5having dimensions of about 50 min. in diameter and 600 mm.llon`g, a ow of nine to eleven cubic feet of gas per hour will be found toy give good results. Gas trap I-I, a 250 ml. tall form 'gas washing bottle, may be interposed between flow'meter and gas inlet 4 -to 'catch any liquid that might blow over shouldthefow meter orifice become clogged. The moisture trap 28 may then be lled with hygroscopic material, for example calcium chlo'- ride. to prevent any moisture vfrom the atmos phere entering housingii.

C'albrationand operation of the cell are as follows: Gas containing moisture content is introduced into the-apparatus through gas inlet! iat a-rate of about 10 cubic feet perhour as indicated by ow meter `2. Recorder 9 is then'placed in operation. Depending on the size of the phosphoric'acid drop 'and its 'degree of hydration, `the cell `will require from '2 to'4 hours to reach equilibrium with the moisture vin the gas. When this has been attained as shown bya fairly constant reading ofthe recorder without any further drift towards the'end of the scale, thecell is calibrated as follows: l l y Disconnect moisture trap 28rfrom gas outlet 2'! `of "cell housing' and attach in its placca tared P295absorptionV bulb, theoutlet of which is connected -to a'dry gasimeter. VPass about`5 4cubic feet of `gas'tl'njough the systernsc that sufficient moisture willlbe'absorbed bythe P205 absorption bulb to give an appreciable Vincrease in weight. Disconnect the P205 bulb and immedireadily calculated. This procedure in substance is the conventional gravitmetrical determination of moisture in gases.

Set recorder 8 to read the moisture content of the gas just found gravimetrically. The recorder will then be in calibration over the entire range of moisture content for that conductivity cell. It is advisable however to run a duplicate gravimetrical determination to make sure that proper adjustment of the recorder has been made. It is then necessary only to run a single gravimetric determination weekly on the cell as a performance check.

There is a time lag between a change ina moisture content of the gas flowing through housing 5 and its indication by recorder 9. Most of this time is required by the phosphoric acid film between electrodes 'l reaching equilibrium with the gas. Thus, the lag is dependent upon phosphoric acid in the nlm and the magnitude of the changes occurring in the moisture content of the gas. The latter is usually small enough to make time lag relatively unimportant.

The apparatus heretofore described may be employed for the continuous recording of moisture in not only contact burner gas but also other gases containing moisture, as for example air, nitrogen, oxygen, hydrogen sulfide, methyl chloride and hydrogen chloride. This apparatus will record moistures of from\0.00l to 0.02 gram of water per cubic foot of gas with an accuracy of $0.001 gram of water per cubic foot. Readings are reproducible.

I have found that if the phosphoric acid film and the gases surrounding it are maintained at a temperature above 50 C. that measurement of moisture in gases containing an excess of 0.03 gram of water per cubic foot of gas can be accurately madebut that the film of phosphoric acid is insensitive to gases containing less than 0.03 gram of water per cubic foot of gas. Furthermore, I have found that while I can obtain accurate recordations of moisture in gases containing less than 0.03 gram water per cubic foot of gas at temperatures below C., the time lag in reaching equilibrium between the film of phosphoric acid and the surrounding gas in unduly long and the results therefore not entirely satisfactory. Therefore, in determining the moisture content of gases containing low concentrations of moisture it is desirable to maintain the temperature of the film of phosphoric acid and surrounding gas between 30 C. and 50 C., preferably about 40 C.

Other hygroscopic materials which may be utilized in my method and apparatus for determining moisture content in gases are lithium chloride, calcium chloride, Zinc chloride and concentrated sulfuric acid. My preferred electrolyte is phosphoric acid since it is not only sensitive to low concentrations of moisture in gases but also relatively inert to corrosive substances such as sulfur dioxide contained in the contact gas, i. e. no material change in resistance of the phosphoric acid ilm results due to corrosive components in gas.

The electrodes are preferably made from platinum since this metal is not affected by most corrosive substances and has substantially the same coenicient of thermal expansion as the glass tube through which it passes. Of course, other suitable non-corrosive metal electrodes. for example gold, may be employed when determining the moisture content of corrosive gases. Obviously, electrodes which are subject to corrosion should be used only when the gases 'to be testedcontain no corrosive substances, and also' should not Abe subject to corrosion by the electrolyte used.

A hygroscopic nlm supported on a nonconducting solid between two metal electrodes when used for determining moisture content of gases has a tendency to drift after a short period of operation, that is, the film of electrolyte records inaccurate values of moisture content in the gas apparently dueto the nonconducting -solid support thereby requiring frequent recharging of the hygroscopic material and repeated calibrations. I have discovered that a film offhygroscopic material suspended between two electrodes in the absence of a support will retain its accuiacy for measuring moisture in gases for long periods of time without recharging, requiring only infrequent performance checks.

.My apparatus as illustrated in the drawings and previously described was employed for the determination and control of moisture in sulfuric acid process gases. A stream of the gases atthe rate of l0 cubic feet per hour and maintained at 40 C. was passed in contact with a drop of phosphoric acid in the absence of a solid support, suspended between two platinum electrodes during a period of 51/2 months and the electrical conductivity of the phosphoric acidras an index of the'moisture contentV in the gases was recorded at intervals of less than ten minutes. Checks against gravimetric moisture determinations over the 5% months period of operation of the apparatus showed the maximum deviation to be only 0.002 gram water per cubic foot of gas. Recharging with phosphoric acid and recalibration were found unnecessary during this test period.

Although certain preferred embodiments of the invention have been disclosed for purposes of illustration it will be evident that various changes and modifications may be made therein without departing from the scope and spirit of the invention.

I claim:

1. Apparatus for determining moisture in gases which comprises a glass housing having a gas inlet and a gas outlet, a heating jacket surrounding the housing near its inlet end adapted to elevate gases entering the housing to a desired temperature, a second heating jacket surrounding the housing for thermostatically maintaining a constant temperature therein, a removable hollow glass tube of smaller diameter than the housing extending into the housing, two spaced platinum wires passing through the interior of the tube out through sealed joints onto the surface of the tube to form a pair of exposed platinum electrodes thereon separated by a distance of between about 0.5 and 1.0 mm... an unsupported film of phosphoric acid suspended between the platinum electrodes which film is exposed to moisture containing gases passing through the housing thereby varying the moisture content of the phosphoric acid with changes in moisture content of the gases passing therethrough, and electrical measuring :means connected to the platinum wires in the tube for determining the electrical conductivity of the lm of phosphoric acid as an index of the moisture content in the gas.

2. Apparatus for determining moisture in gases which comprises a housing having a gas inlet and a gas outlet, two narrowly spaced electrodes contained in said housing. a. liquid electrolyte insolution las-'an index .of the .moisture Acontent .in the gas.

i3. :Apparatus .for .determining moisture `in gases .-whichscomprises a fhousing l'having a 4gas n'lei'fand.rv agas outlet, two narrowly spaced electibdes-Jcontainedfin .said zhousing, a lliquid drop of yan'aqueousfphosphoric :acid solutionsuspended y-hefstweer'ilthe fele'ctrodes and-ih'avingvno other-'support, which Vliquid idrop fof 'fph'o'sphoric acid f solultion "is exposed to -moisture containing gases 'passing through thehousingthereby varying Athe mcisture content of the liquid dropof phosphor- `l`icfacid solution :with changes in moisture content ofthe gases passing therethrough, and means rfor determining theiconductivity of the liquid vdrop of phosphoric acid solution 'as an index ofthemois'ture vcontent inthe gas.

Apparatus for determining moisture in gases ywhich comprises -a housing having ."a'ga's inlet-and aagasoutiet, aheatin'g jacket surrounding the housing adapted 'to .maintain .aconstant temperature therein, two electrodes .separatedgby a distance of between about 0.5 Aand '-1.0 `nini. contained in said housing, a -1iquid:-drop oan aqueous Yiphosphoric acid solution ,suspended'between the electrodes and having no 4other sup.

port, which liquididrop otphosphorc .acid solution is vexposed to moisture containing gases passing through the housing thereby varyingthe moisture content of the liquid drop of phosphoric Aacid solution with changes .in moisture content of the gasesrpassing therethrough, and means for determining the `conductivity of Athe liquid drop of yphosphoricacid solutionfas lan in# dex of the moisture content inthe gas.

. coimas. 'HAYWoRrn `Riemann.ces CITED The `following references .are of record "in the Vle of 'this patent:

UNITED STATES PA'IENTs Number Name Date 1,942,934 Reeve -Jan. 9, y1934 2,002,101 Valby-,et a1. ,.-.m May-21, 1935 .2,061,424 Hutton ..Nov..17, 1936 2,377,426 Kersten June. 5`,s1945 2,458,348 Cleveland Jan. 4,. 1949 2,492,763 

1. APPARATUS FOR DETERMINING MOISTURE IN GASES WHICH COMPRISES A GLASS HOUSING HAVING A GAS INLET AND A GAS OUTLET, A HEATING JACKET SURROUNDING THE HOUSING NEAR ITS INLET END ADAPTED TO ELEVATE GASES ENTERING THE HOUSING TO A DESIRED TEMPERATURE, A SECOND HEATING JACKET SURROUNDING THE HOUSING FOR THERMOSTATICALLY MAINTAINING A CONSTANT TEMPERATURE THEREIN, A REMOVABLE HALLOW GLASS TUBE OF SMALLER DIAMETER THAN THE HOUSING EXTENDING INTO THE HOUSING, TWO SPACED PLATINUM WIRES PASSING THROUGH THE INTERIOR OF THE TUBE OUT THROUGH SEALED JOINTS ONTO THE SURFACE OF THE TUBE TO FORM A PAIR OF EXPOSED PLATINUM ELECTRODES THEREON SEPARATED BY A DISTANCE OF BETWEEN ABOUT 0.5 AND 1.0 MM., AN UNSUPPORTED FILM OF PHOSPHORIC ACID SUSPENDED BETWEEN THE PLATINUM ELECTRODES WHICH FILM IS EXPOSED TO MOSITURE CONTAINING GASES PASSING THROUGH THE HOUSING THEREBY VARYING THE MOSITURE CONTENT OF THE PHOSPHORIC ACID WITH CHANGES IN MOISTURE CONTENT OF THE GASES PASSING THERETHROUGH, AND ELECTRICAL MEASURING MEANS CONNECTED TO THE PLATINUM WIRES IN THE TUBE FOR DETERMINING THE ELECTRICAL CONDUCTIVITY OF THE FILM OF PHOSPHORIC ACID AS AN INDEX OF THE MOISTURE CONTENT IN THE GAS. 